(1) Field of the Invention
The invention relates to antennas, and more particularly to multi-band antennas formed on printed circuit boards.
(2) Description of the Prior Art
With current developments in communication technology, many electronic devices need antennas which can receive and transmit signals in two frequency ranges, three frequency ranges, or more. Commercially, one of major concerns upon those multi-band products is their efficiency, appearance, size, etc. Actually in most communication devices, the efficiency of signal transmission is the most important of all. In particular, the performance of the antenna in the communication device takes a major share to the efficiency of signal transmission. Generally, to achieve a modern appearance design of the communication device without sacrificing the efficiency of antenna has become the major goal to most designers in this industry.
For example, U.S. Pat. No. 6,166,694 to Zhinong Ying, Lund describes a multi-band antenna titled as “Printed Twin Spiral Dual Band Antenna”. As shown in FIG. 1 thereof, the dual band antenna is attached over the printed circuit board (PCB) 1 via a dielectric substrate 2 and is also connected with the PCB 1 through a feeding pin 6 and a grounded post 7. A matching bridge 5 is introduced to connect the feeding pin 6 and the grounded post 7. As shown, the dual band antenna assembly comprises two conductor arms, each of which, a first spiral arm 3 and a second spiral arm 4, is configured in an inner spiral shape. The first spiral arm 3 is tuned to receive lower frequency band signals, while the second spiral arm 4 is tuned to receive higher frequency band signals. Under such an arrangement, the antenna assembly is allowed to operate in multiple frequency bands.
As shown in FIG. 1, a dielectric substrate 2 is positioned between the antenna assembly and the printed circuit board 1. In manufacturing process, an extra process should be increased in order to form the dielectric substrate 2 on the PCB 1. Moreover, the antenna assembly and the main circuit wires of the communication device are manufactured in different processes. If simplifying the manufacturing process is possible, the manufacturing time can be definitely saved. Additionally, an additional space on the PCB 1 is needed for constructing the antenna assembly, and as a consequence layout complexity of the main circuit wires has been increased. Therefore, an easy solution for constructing a multi-band transmission device with a PCB having a built-in planer antenna is surely welcome to the skilled person in the art.